Short answers, pulled from the story.
Flavius Valerius Constantius entered the world on the 31st of March though historians cannot name his birth year. He hailed from Moesia Superior, a Roman province situated on the south bank of the Middle Danube river.
Diocletian allowed Maximian to promote Constantius into a new power sharing arrangement known as the Tetrarchy in 293. On the 1st of March 293 at Mediolanum now Milan Constantius was formally appointed as Maximian's caesar.
Constantius spent two years neutralizing Frankish allies of Allectus while northern Gaul remained under British control. Julius Asclepiodotus led one fleet from the Seine mouth while Constantius launched another from Bononia to defeat Allectus near the Isle of Wight.
From 303 onward Constantius began enforcing imperial edicts dealing with the persecution of Christians but made the least effort to implement decrees in western provinces. He limited himself to knocking down a handful of churches rather than hunting believers according to Lactantius records.
Constantius died suddenly at Eboracum modern-day York on the 25th of July 306. As he lay dying he recommended his son to the army as successor so Constantine was declared emperor by legions stationed at York.